Hendricksons in March? Experts explain some early Michigan trout bugs

Here we are, a whole month ahead of trout opener, and we've been fishing in T-shirts and breathable waders.

The Petoskey average of 67.5 degrees through the first half of March made it feel like you were fishing for a bizarrely strong run of summer Skamania steelhead. It's one of the few times anglers may have had to combat upper-arm sunburn and high rivers from snow-melt at the same time.

And already, some fly anglers are wondering if the warm air temperatures will push the typical schedule of hatch emergences ahead.

"This strange warm-up we've had got our water temperatures unseasonably warm," said Andy Partlo, owner of the Old Au Sable Fly Shop in Grayling. "I caught my first fish on a Hendrickson yesterday. This is the first time I've seen a Hendrickson in March."

Mayfly hatches are largely controlled by water temperature, and Hendricksons usually begin hatching in April and peak in May. The fly shop has been seeing not only its typical springtime fare — midges and black stone flies — but mayflies such as blue winged olives and Hendricksons as well.

But mayflies aren't tied only to temperature. They emerge based on photo period as well, said Ashley Moerke, associate professor of biology at Lake Superior State University in Sault Ste. Marie.

"It's not necessarily a temperature that makes them hatch, but they accumulate heat over time. The heat, along with day length, triggers a hatch," she said.

Insects, like plants, begin developing after their environment reaches a specific temperature. While that basic temperature depends on species, said Moerke, the concept can be applied generally.

"Every species has a different temperature threshold," she said. "Stone flies, for example, can develop at much colder temperatures than mayflies."

Caddis have an even larger variation baseline of temperature at which they begin to develop.

Regardless of the temperature that triggers their growth, the development of all of these bugs is based mostly on water temperature, said Howard Russell, diagnostic entomologist at Michigan State University.

"Since the larvae of aquatic insects develop in water, their development depends on water temperature," he said.

Russell isn't sure we'll see dramatically earlier insect hatches.

"Development depends on water temperature, and even though water is a little warmer than what it would be compared to a normal year, water temps certainly in rivers aren't affected so much by air temperature as it is by ground temperature, snowfall and groundwater," he said. "(Emergences) may be somewhat early, but I wouldn't think weeks and weeks ahead."

Moerke says river temperatures don't swing nearly as wildly as air temperatures.

"With these warm temperatures we've had, more snow-melt is still bringing in water at a pretty cold temperature," she said. "(Aquatic insects) aren't experiencing this huge heat wave like the terrestrial insects would be in the ground. Aquatic insects are buffered in this way."

But, she says, because Michigan has had snow-melt early, trout water will warm up faster for not having a slow, steady stream of snow-melt.

And because of the record-breaking heat of March, and because of the vanished snow-melt, we may see some early bugs, she said — if only a touch early.

"It's difficult to say," she said. "It depends on the weather from here on out. If the weather is normal, hatches could be a couple weeks earlier. But if it's a really cold spring, that might delay them again."

Partlo thinks the insect hatches will even out.

"The heat kick-started early-season hatches, but I expect June hatches to be about normal," he said. "I expect that the river kind of takes care of itself."